With the trend towards miniaturization of electronic products, electronic chips also become thinner and thinner. When a Silicon wafer is thinned to a thickness of 100 microns or less, however, it may easily break or bend due to stress applied thereon during processing. As a result, it is almost impossible to process such an ultra-thin wafer directly. In order to process an ultra-thin wafer, it usually needs to be temporarily bonded to a carrier wafer. While the ultra-thin wafer and the carrier wafer are bonded together as one piece, the ultra-thin wafer can be subjected to processes such as thinning, and formation of TSVs, re-distribution layers, and internal interconnections. Then, the ultra-thin wafer and the carrier wafer are separated from each other, and the thinned wafer is cleaned and cut into individual chips, thereby completing the processing of the ultra-thin wafer.
At present, a device wafer is generally bonded to a carrier wafer by coating a layer of adhesive therebetween and then bonding them to each other in a bonding machine. A process of separating the bonded device wafer and carrier wafer is known as de-bonding.
Generally, there are several methods to de-bond the temporarily bonded wafers. A first method is to dissolve the bonding adhesive in a solvent from the edge of the bonded device wafer and carrier wafer. A second method is to separate them by thermal shearing. With the first method, the solvent dissolves the bonding adhesive slowly from the edge of the junction where the device wafer and carrier wafer are bonded together, and it will take a long time for the solvent to reach the center of the device wafer, resulting in a very low efficiency. In addition, it needs a special plate to secure the device wafer so as to prevent the device wafer from mixing with the carrier wafer while separating them, which causes a complex procedure and a high cost. As to the second method, it needs a special equipment to carry out the thermal shearing process, which also causes a high cost, and the thermal shearing process is easy to damage the device wafer and thus has a low yield.
In view of the above, the inventors proposed a wafer de-bonding method in which a surface of the carrier wafer is treated and an isolation film is formed thereon. The isolation film is adhered to the carrier wafer with a proper adhesion force so that it would not fall off the carrier wafer if nobody tears it intentionally, but it would be peeled off from the carrier wafer if somebody tears it with a force. Then, a layer of adhesive may be coated between the front surface of the carrier wafer with the isolation film thereon and a device wafer so as to bond them together. The inventors also proposed a wafer de-bonding method in which a gas jet generator produces a gas jet towards a junction between the device wafer and the carrier wafer so as to separate them. However, the inventors found out that it still needs a wafer de-bonding device with a high degree of automation and simple and convenient operations in order to meet requirements of industrial production.